Question about down shifting from fifth to third

[xyz999]

Hey guys,

What's the most effective way to down shift from fifth to third?

Down the rocky road big straight at Calabogie, I would downshift from fifth to third directly with one blip of throttle. The gear will always go into third and rarely gives me any problem. But at Mosport into 5a, I would try to do the same and sometimes the gear won't go into third. I understand 5a is a tricky corner with a short braking zone and a lot of deceleration and trail braking, but how come my shifter doesn't go into gear even when my clutch is disengaged? Is it because I may be downshifting too early and so the output shaft (vehicle speed) is too fast for third gear to engage? but clutch is disengaged though. Can anybody help explain the mechanic here please.

Also, please consider the two videos of really good drivers below. The BMW driver would downshift from fifth to fourth, blip, then fourth to third, blip, and engage clutch. I couldn't tell precisely from Kyle Marcelli's video as there is no foot cam, but it looks like he's doing the same too at 5a. My question is what is the point of going into fourth since eventually they are going to be in third? Also, the BMW driver did not even release the clutch after the first blip of throttle, what's the point? It looks to me it's just extra footwork. Can anybody shed some light on "proper maneuver", or is it partly car set up and partly personal preference?

Kyle Marcelli Mosport:
https://www.youtube.com/watch?v=Z5xJ2_L82j0
Nurburgring BMW M3:
https://www.youtube.com/watch?v=CaQNCR3qXzQ

[Steven Scala]

Re: Question about down shifting from fifth to third

I generally drop only one gear for 5A, as (if I've carried enough speed through A) the short goose of throttle between A and B is practically maintenance throttle, so mid-range is good enough. I get the second downshift at 5B. YMMV.

[wings2k]

Re: Question about down shifting from fifth to third

Double downshift here, prevents going into the wrong gear.

[wparsons]

Re: Question about down shifting from fifth to third

I generally drop only one gear for 5A, as (if I've carried enough speed through A) the short goose of throttle between A and B is practically maintenance throttle, so mid-range is good enough. I get the second downshift at 5B. YMMV.

I find the same works for me.

As for why it won't go into gear, how solid are the transmission mounts? Is it possible the gearbox is moving and jamming up the shifter linkage? There would be more lateral forces on the gearbox coming into 5a than in the corners at Calabogie.

[Slowpoke]

Re: Question about down shifting from fifth to third

I do it the same as Mr. Scala, but consider that the other caers might have dog gears.

[xyz999]

Re: Question about down shifting from fifth to third

I generally drop only one gear for 5A, as (if I've carried enough speed through A) the short goose of throttle between A and B is practically maintenance throttle, so mid-range is good enough. I get the second downshift at 5B. YMMV.

I find the same works for me.

As for why it won't go into gear, how solid are the transmission mounts? Is it possible the gearbox is moving and jamming up the shifter linkage? There would be more lateral forces on the gearbox coming into 5a than in the corners at Calabogie.

I was actually thinking about trying it next time, but on a time attack line into 5b ideally I don't think you need to be on throttle at all though. I mean if you are on throttle then chances are that means you are not going into 5b fast enough right? For the record, I don't do that because I find I slide too much and margin of error is too small. I just thought that would be really fast. Maybe I will try it out one day.

But still, why the pros do two sequential downshift instead of one? especially when the clutch is not released between the gear shift as shown in the second video. Even more so why blip the throttle to rev match if you are not releasing the clutch?

I do it the same as Mr. Scala, but consider that the other caers might have dog gears.

Are you saying dog gears would prevent driver from going to third directly from fifth? How does that work.

[Steven Scala]

Re: Question about down shifting from fifth to third

... how solid are the transmission mounts? Is it possible the gearbox is moving and jamming up the shifter linkage? There would be more lateral forces on the gearbox coming into 5a than in the corners at Calabogie.

I've found that OEM-soft FWD engine/gbx mounts often balk up the 2-3 upshift coming onto SMP's frontstraight. Drivetrain tilt plus a critical cross-gate shift there, so I often delay unwinding some steering input until the shift, during which I straighten the steering a little, for a very short time. Maybe superstition, maybe helps. I dunno.

... on a time attack line into 5b ideally I don't think you need to be on throttle at all though. I mean if you are on throttle then chances are that means you are not going into 5b fast enough right? For the record, I don't do that because I find I slide too much and margin of error is too small. I just thought that would be really fast. Maybe I will try it out one day.

In FWD at least, I have to give a bit of throttle between 5A and B in order to avoid chucking myself backward into the tire wall after cresting 5A. I'd have carried some braking into the 5A turn-in, probably to outbrake some obdurate who insists that trail braking is the devil's voodoo. While 5A's uphill entry tolerates my oversteer-pedal silliness, the grade advantage (Mosport loves FWD) doesn't last forever, so a one-count of the understeer pedal at the crest just to save my life and whatnot.

This is vastly exaggerated on cold tires too, so I'd factor that into a time-attack strategy.

But still, why the pros do two sequential downshift instead of one? especially when the clutch is not released between the gear shift as shown in the second video. Even more so why blip the throttle to rev match if you are not releasing the clutch?

Didn't watch the videos, but if Marcelli's vid is in Lites or Pro Mazda, that's a sequential box, which in its fundamental operation precludes any possibility of a skip-shift of any sort.

Are you saying dog gears would prevent driver from going to third directly from fifth? How does that work.

This is a case of 'every pope's catholic, but not every catholic's the pope': almost without exception, a sequential racing box has straight-cut gears with dog-ring engagement. The skip shift's impossible because sequential, not because dogring.

There are also straight-cut, h-gate dog 'boxes like in F1600s, (for now) F2000s, and the nascars. Some might say they're a dying breed, though I'd still consider them a demon tweak. They're actually the best suited for a downward skip-shift, with no synchros to mismatch engagement with the bigger blip. 4-2 downshifting a Hewland is a really nice feeling when it's right.

[John P]

Re: Question about down shifting from fifth to third

I have used both methods. In 5A shift to 4th on uphill and then to 3 going into 5b. Going from 5 to 4 to 3rd, I find it easier on the Tranny. Shifting diectly from 5 to 3 isn't something the manufacturer expected, so there is a chance of missing 3rd and going into 1st, (which can cause a blown engine on a Front drive car or a spin on a rear wheel drive). Found on a FF, shifting from 4th to 2nd is pretty natural (has a Hewland race box without a fifth gear).

JohnP